Damage‐Free Charge Transfer Doping of 2D Transition Metal Dichalcogenide Channels by van der Waals Stamping of MoO₃ and LiF

Abstract

To dope 2D semiconductor channels, charge‐transfer doping has generally been done by thermal deposition of inorganic or organic thin‐film layers on top of the 2D channel in bottom‐gate field‐effect transistors (FETs). The doping effects are reproducible in most cases. However, such thermal deposition will damage the surface of 2D channels due to the kinetic energy of depositing atoms, causing hysteresis or certain degradation. Here, a more desirable charge‐transfer doping process is suggested. A damage‐free charge‐transfer doping is conducted for 2D MoTe2 (or MoS2) channels using a polydimethylsiloxane stamp. MoO3 or LiF is initially deposited on the stamp as a doping medium. Hysteresis‐minimized transfer characteristics are achieved from stamp‐doped FETs, while other devices with direct thermal deposition‐doped channels show large hysteresis. The stamping method seems to induce a van der Waals‐like damage‐free interface between the channel and doping media. The stamp‐induced doping is also well applied for a MoTe2‐based complementary inverter because MoO3‐ and LiF‐doping by separate stamps effectively modifies two ambipolar MoTe2 channels to p‐ and n‐type, respectively.

Molecular Doping Enabling Mobility Boosting of 2D Sn2+‐Based Perovskites

“…[29] Molecular doping is a universal method to modulate the electrical properties of diverse semiconductors, including organics, oxides, and nanomaterials. [40][41][42][43][44] Molecular dopants with a wide range of ionization energies and electron affinities can induce charge transfer from the host material to the dopant layer without deteriorating the host lattice microstructure. [28,45,46] However, the blending method makes it difficult to distinguish the origin of doping from the dopant or grain boundary passivation.…”

High-Performance WSe2 Top-Gate Devices with Strong Spacer Doping

“…A HAuCl 4 doping concentration higher than 6.7 × 10 12 cm –2 did not substantially reduce the mobility of the channel. This result can be attributed to the surface charge transfer doping mechanism of HAuCl 4 , which does not damage the structure of WSe 2 . , The mobility decreased marginally to 95 cm 2 V –1 s –1 in the heavy-doping case because of the charged impurity scattering and short-range scattering of high-concentration holes in the channel. , With a high doping concentration and mobility, we can obtain a record-high sheet conductivity (0.4 mS) in the monolayer WSe 2 . This sheet conductivity is the critical parameter when considering the spacer doping in the top-gate devices.…”

“…This result can be attributed to the surface charge transfer doping mechanism of HAuCl 4 , which does not damage the structure of WSe 2 . 39,40 The mobility decreased marginally to 95 cm 2 V −1 s −1 in the heavy-doping case because of the charged impurity scattering and shortrange scattering of high-concentration holes in the channel. 40,41 With a high doping concentration and mobility, we can obtain a record-high sheet conductivity (0.4 mS) in the monolayer WSe 2 .…”

Defect Engineering of MoTe2 via Thiol Treatment for Type III van der Waals Heterojunction Phototransistor

“…Endeavors to achieve high performance stable p-type MoTe 2 FETs have been ongoing, by employing numerous methods, such as physisorption of oxygen containing molecules and surface charge transfer using functional polymers and MoO 3 oxide. − For example, Chang et al achieved reversible p/n-type doping of MoTe 2 transistors by physisorbing O 2 or H 2 O on the air-sensitive MoTe 2 channel surface . In another report, Ke et al demonstrated p-doping of MoTe 2 FETs through damage-free laser irradiation on multilayer MoTe 2 in a localized channel area .…”

“…However, these surface charge transfer p-doping methods on MoTe 2 flakes have primarily been applied to single-channel devices rather than a heterostacked channel. In other words, despite the improved electrical performances of p-MoTe 2 in terms of hole carrier concentrations, several unresolved issues persist, including limited device operations under inert conditions and lack of applicability due to thick polymer layers coating the MoTe 2 nanosheets. − Moreover, beyond single-channel MoTe 2 device, further extended devices or practical applications have rarely been reported, although it would be equally important to fully exploit the p-type semiconducting properties in complex heterojunction systems. , …”